package 算法.leetcode.offer;

import java.util.Stack;

/**
 * 用两个栈实现一个队列。队列的声明如下，请实现它的两个函数 appendTail 和 deleteHead ，
 * 分别完成在队列尾部插入整数和在队列头部删除整数的功能。(若队列中没有元素，deleteHead 操作返回 -1 )
 *
 *  
 *
 * 示例 1：
 *
 * 输入：
 * ["CQueue","appendTail","deleteHead","deleteHead"]
 * [[],[3],[],[]]
 * 输出：[null,null,3,-1]
 * 示例 2：
 *
 * 输入：
 * ["CQueue","deleteHead","appendTail","appendTail","deleteHead","deleteHead"]
 * [[],[],[5],[2],[],[]]
 * 输出：[null,-1,null,null,5,2]
 *
 * @author lchenglong
 * @date 2022/3/16
 */
public class Offer09 {

    static class CQueue {

        Stack<Integer> in;

        Stack<Integer> out;

        public CQueue() {
            in = new Stack<Integer>();
            out = new Stack<Integer>();
        }

        public void appendTail(int value) {
            in.push(value);

        }

        public int deleteHead() {
            if (!out.empty()) {
                return out.pop();
            } else {
                while (!in.empty()){
                    out.push(in.pop());
                }
                return out.empty()?-1:out.pop();
            }
        }
    }

    public static void main(String[] args) {
        CQueue cQueue = new CQueue();
        int res = cQueue.deleteHead();
        System.out.println(res);
        cQueue.appendTail(5);
        cQueue.appendTail(2);
        res = cQueue.deleteHead();
        System.out.println(res);
        res = cQueue.deleteHead();
        System.out.println(res);
    }
}
